1. Field of the Invention
Embodiments of the invention generally relate to the fabrication of solar, semiconductor, and electronic devices, and more particularly to mesa etch methods and compositions, as well as to epitaxial lift off (ELO) devices and methods.
2. Description of the Related Art
One phase in device fabrication involves handling and packaging of thin films used as solar devices, semiconductor devices, or other electronic devices. Such thin film devices may be manufactured by utilizing a variety of processes for depositing and removing materials onto a wafer or other substrate. One uncommon technique for manufacturing thin film devices is known as the epitaxial lift off (ELO) process. The traditional ELO process includes depositing an epitaxial layer or film on a sacrificial layer on a growth substrate, then etching the sacrificial layer to separate the epitaxial layer from the growth substrate. The thin epitaxial layer removed is known as the ELO film or layer and typically includes thin films used as solar devices, semiconductor devices, or other electronic devices.
The thin ELO films are very difficult to manage or handle, such as when bonding to a substrate or while packaging, since the ELO films are very fragile and have narrow dimensions. The ELO films crack under very small forces. Also, the ELO films are very difficult to move due to their extremely narrow dimensions.
The speed of the overall process may be limited by the lack of delivery or exposure of reactant to the etch front, which leads to less removal of by products from the etch front. The etching process may be a diffusion limited process and if the films were maintained in their as deposited geometries, a very narrow and long opening or crevice would form and severely limit the overall speed of the process. Reactants move towards the etch front while by-products generally move away from the etch front.
The etching process must be fast in order to obtain high throughput of the overall fabrication process, as well as to reduce the duration in which the epitaxial layer is under undue strain or force. Therefore, the etch solution must be aggressive at removing targeted materials, but also selective, so not to etch non-targeted materials. Low throughput may be experienced if the etch solution is not very chemically aggressive or too dilute. Also, the wafers must also not be over-etched, contaminated, or otherwise damaged during the ELO etching process. The wafers, especially gallium arsenide wafers, are valuable and ideally would be used through many cycles of depositing and removing materials from the surface of the wafer.
Therefore, there is a need for alternative etching compositions and methods used during device fabrication, such as during an ELO process.